Heat 1 tablespoon of vegetable oil in a large pot over high heat. Char 2 halved onions and 1 piece of ginger, 2in / 5cm long, sliced.
Add 2 liters of water, 1.5kg of bone-in, skin-on chicken thighs, 5 whole star anise, 1 cinnamon stick, 4 whole cloves, 2 teaspoons of fennel seeds, and 2 teaspoons of coriander seeds.
Stir in 8 teaspoons of fish sauce, 6 teaspoons of sugar, and ¾ teaspoon of salt. Bring to a simmer, skim off the foam, and simmer very gently for 1½ hours.
Lift out the chicken and shred the meat. Strain the broth and add salt until it tastes slightly strong.
Cook 360g of dried thin flat rice noodles according to the package. Divide between bowls, top with the chicken, and ladle over the hot broth.
